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Friday, July 30, 2010

Recently I completed a trade (specimens to be shown in the next post) with Dan B. who sent me some interesting Cambrian Trilobite fossils from Tanglefoot Creek, BC, Canada. While I was preparing a post to show off some of the pieces he sent me, I asked him about the formation, it's geology and the history of the site. He directed me to several good resources and related a fair amount of personal knowledge as well. It was then that I decided that I was not the best person to write about these fossils since I had not collected them. I asked Dan if he'd like to write a blog post about them and he obliged with the following:

The McKay Group Trilobite Locality of Southeastern British Columbia.

Tucked away in the Southeastern corner of British Columbia not far from the historic town of Fort Steele, outcrops a highly fossiliferous exposure of the McKay Group. The site often referred to as the Tanglefoot Creek Trilobite Locality, for its location on an unnamed tributary of Tanglefoot Creek, is a very special place. Below are two photographs of the site.

Along the upper reaches of this creek lay the scattered remains of hundreds of oddly preserved trilobites from the Upper Cambrian (Upper Steptoean, 494.5-493 Ma). Odd is a perfect description for the mode of preservation of the Tanglefoot Creek trilobites, for each perfect trilobite is faithfully reproduced by vertical encrustations of parallel to sub-parallel crystals of calcite that have grown from the dorsal and ventral surfaces of the trilobite. These calcitic growths form neat little wafers that weather from the marly limestones exposed at the site. Occasionally these calcite wafers grow together forming sheet-like structures. Although this mode of preservation is strange it is reminiscent of that of the Middle Cambrian trilobites found in the Wheeler Formation of Utah, however those trilobites do not occur on wafers.

Typical calcite wafers.

Several wafers that have grown together. Wujiajiania sutherlandi.

Complete trilobites are a rarity at most Cambrian sites but at the Tanglefoot Creek site the vast majority of specimens are either fully complete (i.e. carcasses) or missing their free cheeks (i.e. moults). Partial specimens do occur but the large numbers of complete specimens overshadow these.

Large wafer with Labiostria westropi.

The trilobite fauna at Tanglefoot Creek shows a fair amount of diversity. There are ten genera with 11 species commonly found at the site. By far the most common species encountered are Wujiajiania sutherlandi and Labiostria westropi.

Wujiajiania sutherlandi

Labiostria westropi

The next most commonly encountered species are Pterocephalia norfordi, Irvingella major and Pseudagnostus communis.

Additionally there are very rare specimens of Homagnostus sp. and Cliffia c.f. lataegenae . As these species are rarely encountered, I do not have photos of either specimen.

Since the publication of the site's location by researchers at the University of Alberta (B.D.E. Chatterton) and Denman Island (R. Ludvigsen) in 1998 the area has been staked as a mineral lease. As such collecting is no longer allowed at the site but numerous other localities nearby have been found outside the lease area. These new sites rival the original Tanglefoot Creek locality in terms of trilobite diversity. Current research on these new sites and their associated trilobite faunas is being undertaken at the University of Alberta and a paper is forthcoming.

For further information on this remarkable locality and its trilobite fauna see the sources below.

Monday, July 26, 2010

Leiopteria is one of the many common Pelcypods found in the Mahantango. It's shell is rounded with a very long hinge line that gives it a look like it has wings. Leiopteria primarily existed from the Silurian to the middle Carboniferous, but seems to be most prolific in the middle to upper Devonian.

Here is an internal mold (front and back) of a shell.

Another internal impression preserved in rock.

Leiopteria belonged to the extinct family Pterineidae within the order Pterineidae. According to Wikipedia, modern families of the order Pterineidae are important economically since they are cultivated as pearl oysters (although they are not at all related to true oysters nor to pearl bearing freshwater mussels). Below is a modern Akoya pearl oyster from Japan. You can see that it has a similar body plan with "wings" along the hinge line.

Some other genera from the Pterineidae that are also found in the Mahantango are:

Cornellites

Leptodesma (with a Leiopteria above it)

Actinopteria

The Deep Blue server at the University of Michigan has a great paper regarding Leiopteria with some excellent plates illustrating specimens from the Arkona region.

Saturday, July 24, 2010

Another very common Brachiopod from the Middle Devonian is Athyris. In the Mahantango formation it's very common in the Montebello member. This member is a fairly near shore series of upwards fining (grain size decreasing as you go up the stratigraphic column) rocks. I'll discuss this more in another post. A good exposure of the Montebello member is at an old quarry on the east side of the Susquehanna, north of Harrisburg, PA near a small town called Ft. Hunter. In some isolated beds the conditions were right to allow abundant life and Athyris is a major player.

This is a typical specimen that is complete and has some recrystallized shell still remaining. The last picture show the exterior shell cast contained in the shale matrix.

One of the most interesting occurances at the Ft. Hunter site is that some of the Athyris have their Lophophore supports (called the brachidium) preserved. This is somewhat uncommon to find as they are fairly delicate, spiral shaped structures. To be able to find a specimen with these structures presevred indicates calm conditions and very rapid burial before the two valves can separate after death.

Below are some examples of specimens I've found from the site with the Spiralia preserved.

From another part of the Mahantango, the Sherman Creek member, comes these two internal molds of Athyris. Notice the variations between the molds which could indicate different species.

For more info on the internal anatomy of Brachiopods (it's more than I can post about) check out this page from SUNY Courtland

Mike over at Louisville Fossils recently posted about this same Brachiopod with images of fossils from his region and some that I sent him from upstate NY. I'm cheating with that last link as I haven't taken pics of any specimens I found from that site for myself yet.

Thursday, July 22, 2010

Edit 11/17/15: Thanks to Steve Pavelsky, who commented on facebook regarding these fossils, for recognizing them as the rare bryozoan, Ptylipora sp. (possibly striata).

I was doing research for a trip up to NY and Ontario last April and was reading through Karl Wilson's excellent website "New York Paleontology" website and I came across a page talking about the Hoxie Gorge. On the page they talk about a rare fossil that is relatively common at this site call Plumalina. As I was reading and looking at the pictures I realized that I'd found something similar twenty years ago when I was a kid exploring a local Devonian Mahantango formation exposure. I'll go into more detail about the site another time but here is the fossil:

Here is a pic from the aforementioned website for comparison:

You can also see some superb pics on this Flickr page: Click Here

Seems that this might have been related to Hydrozoans. I'd previously thought it was part of a Conularia but it doesn't look right. I even asked someone at the Smithsonian to take a look at it years ago but they said there wasn't enough to make a determination.

Recently I think I found another example of this rare fossil in the rocks of the Mahantango formation (Centerfield member) near Stroudsburg, PA. This specimen is a faint impression that is best seen with the light at an oblique angle. Below are pictures of the specimen taken from different angles to highlight the herringbone like structure:

I don't think these are Crinoid pinnules as they are much too long and unsegmented. Maybe they are leaves that are partially decomposed? At any rate, it is interesting how one can recognize a fossil that is in their collection just by looking at other people's pictures.

About Me

I'm a 40-something, life long student of Geology living in Philadelphia. My interests include Photography, Architecture and History among other things. When not cleaning my recent finds you'll find me in my backyard Hybridizing Daylilies or working in my garden. This Blog is an outlet for me to express my interest in fossils, catalog my collection and coalesce my thoughts and research into a useful medium.